Computing the nearest polynomial with a zero in a given domain by using piecewise rational functions

  • Authors:
  • Hiroshi Sekigawa

  • Affiliations:
  • -

  • Venue:
  • Journal of Symbolic Computation
  • Year:
  • 2011

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Abstract

For a real univariate polynomial f and a closed complex domain D whose boundary C is a simple curve parameterized by a univariate piecewise rational function, a rigorous method is given for finding a real univariate polynomial f@? such that f@? has a zero in D and @?f-f@?@?"~ is minimal. First, it is proved that the minimum distance between f and polynomials having a zero at @a@?C is a piecewise rational function of the real and imaginary parts of @a. Thus, on C, the minimum distance is a piecewise rational function of a parameter obtained through the parameterization of C. Therefore, f@? can be constructed by using the property that f@? has a zero on C and computing the minimum distance on C. We analyze the asymptotic bit complexity of the method and show that it is of polynomial order in the size of the input.